The present invention relates to optical add/drop multiplexer devices, and more particularly, an optical add/drop multiplexer (OADM) using a large diameter waveguide for dynamically adding and dropping optical signals from a WDM optical signal.
The telecommunications industry is undergoing dramatic changes with increased competition, relentless bandwidth demand, and a migration toward a more data-centric network architecture. First generation point-to-point wave division multiplex systems have eased the traffic bottleneck in the backbone portion of a network. As a new cross-connect architecture moves the technology closer to the subscriber side of the network, operators are challenged to provide services at the optical layer, calling for more flexible networks that can switch and reroute wavelengths. This is placing great emphasis and demand for wavelength agile devices, of which compression-tuned grating devices could play a major role.
The need to provide services xe2x80x9cjust in timexe2x80x9d by allocation of wavelengths, and further migration of the optical layer from the high-capacity backbone portion to the local loop, is driving the transformation of the network toward an all optical network in which basic network requirements will be performed in the optical layer.
The optical network is a natural evolution of point-to-point dense wavelength division multiplexing (DWDM) transport to a more dynamic, flexible, and intelligent networking architecture to improve service delivery time. The main element of the optical network is the wavelength (channel), which will be provisioned, configured, routed, and managed in the optical domain. Intelligent optical networking will be first deployed as an xe2x80x9copaquexe2x80x9d network in which periodic optical-electrical conversion will be required to monitor and isolate signal impairments. Longer range, the optical network will evolve to a xe2x80x9ctransparentxe2x80x9d optical network in which a signal is transported from its source to a destination totally within the optical domain.
A key element of the emerging optical network is an optical add/drop multiplexer (OADM). An OADM will drop or add specific wavelength channels without affecting the through channels. Fixed OADMs can simplify the network and readily allow cost-effective DWDM migration from simple point-to-point topologies to fixed multi-point configurations. True dynamic OADM, in which reconfiguration is done in the optical domain without optical-electrical conversion, would allow dynamically reconfigurable, multi-point DWDM optical networks. This dynamically reconfigurable multi-point architecture is slated to be the next major phase in network evolution, with true OADM an enabling network element for this architecture.
One known commercially is a fixed all-optical OADM that couples fixed optical channel filters, usually fiber Bragg gratings, to passive optical routing and branching components such as couplers and circulators. The fiber Bragg gratings are not tuned to filter different wavelengths.
A tunable grating/circulator approach for dynamically reconfigurable OADM has also been pursued in the prior art by thermal or strain tuning the grating. These dynamic or programmable all-optical OADM designs are based on tunable gratings. But thermal tuning is slow and difficult to maintain and control wavelength to the tolerances required in current DWDM systems that feature sub-nanometer channel spacing. Strain tuning approaches, in which the fiber grating is mechanically stretched, have also proved difficult to maintain and control and tune wavelengths due to fiber attachment challenges and slight mechanical creep that cause errors and slippage. The reliability of a fiber being held under tension for extended periods of time is questionable and controversial for use in the industry.
Ball, in U.S. Pat. No. 6,020,986, shows an add/drop module having a circulator 16, an array of tunable fiber Bragg gratings, a piezoelectric device and a controller, which is incorporated herein by reference. Strain is applied by coupling the piezoelectric device to each fiber Bragg grating, and adjusting the current applied to each piezoelectric device from the controller. The wavelength of the grating may be adjusted (xe2x80x9ctunedxe2x80x9d) in the nanometer range for gratings having a wavelength of about 1540 nanometers. However, Ball does not disclose how the piezoelectric device is physically coupled to the fiber Bragg gratings to apply strain. See also U.S. Pat. No. 5,579,143, issued to Huber, and U.S. Pat. No. 5,748,349, issued to Mizrahi, which disclose OADM systems having tunable optical filters, which are incorporated herein by reference.
Moreover, the grating/circulator approach for OADM has emerged as a viable method over other OADM techniques such as optical switches and arrayed waveguide devices, which are broadband in nature. Combinations of switches and wavelength multiplexers achieve wavelength, selection but suffer from other performance problems such as high optical losses and high cost.
Despite intense efforts, dynamic OADMs of such types remain elusive due to inherent performance issues, particularly drift and reliability, than thermal or tension grating tuning approaches. The inadequacy of thermal and tension-based grating tuning methods to control and maintain wavelength to tight tolerances would require some sort of in-line signal diagnostic, such as a wavelength monitoring device or spectrum analyzer, to provide feedback and referencing for closed loop control of the grating wavelength.
In accordance with an embodiment of the present invention, an optical drop filter includes a compression-tuned optical device. The compression tuned optical device includes an optical waveguide, which has an inner core disposed within an outer cladding and a grating disposed within the inner core. The grating reflectd a first reflection wavelength of light back along the inner core and propagates the remaining wavelengths of light through the grating. The optical waveguide includes a pair of opposing surfaces. The optical waveguide also includes a compressing device that compresses the optical waveguide for compressing the opposing surfaces towards each other to tune the grating and change the reflection wavelength of light reflected back along the inner core. The drop filter also includes an optical directing device for providing an input optical signal to the compression-tuned optical device. The input optical signal has a plurality of optical channels centered at spaced wavelengths. The compression-tuned optical device removes an optical channel from the input optical signal.
In accordance with another embodiment of the present invention, an optical add filter includes a compression-tuned optical device, which has an optical waveguide. The optical waveguide includes an inner core disposed within an outer cladding and a grating disposed within the inner core. The grating reflects a first reflection wavelength of light back along the inner core and propagates the remaining wavelengths of light through the grating. The optical waveguide includes a pair of opposing surfaces. A compressing device compresses the opposing surfaces of the optical waveguide to tune the grating and change the reflection wavelength of light reflected back along the inner core. An optical directing device is optically connected to the compression-tuned optical device for combining an input optical signal and an added optical channel. The input optical signal has a plurality of optical channels centered at spaced wavelengths. The compression-tuned optical device provides the optical channel to be combined with the input optical signal to provide a combined output signal.
In accordance with another embodiment of the present invention, an optical add/drop multiplexer includes a compression-tuned optical device that has an optical waveguide. The optical waveguide includes an inner core disposed within an outer cladding and a grating disposed within the inner core. The grating reflects a first reflection wavelength of light back along the inner core and propagates the remaining wavelengths of light through the grating. The optical waveguide includes a pair of opposing surfaces. A compressing device compresses the optical waveguide to compress the opposing surfaces towards each other to tune the grating and to change the reflection wavelength of light reflected back along the inner core. An optical directing device is optically connected to the compression-tuned optical device for combining an input optical signal and an added optical channel. The input optical signal has a plurality of optical channels centered at spaced wavelengths. The compression-tuned optical device provides the optical channel to be combined with the input optical signal to provide a combined output signal.
In accordance with another embodiment of the present invention, a compression-tuned optical add/drop module includes a compression device for providing a compression force applied along an axis of compression. A grating compression unit having a grating along the axis of compression is responsive to the optical input signal, and further responsive to the compression force, for providing a grating compression unit optical signal having the selected wavelength of the channel to be added to or dropped from the input signal.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.